Semiconductor device with impurity region with increased contact area

ABSTRACT

A semiconductor device includes a semiconductor substrate, an impurity region in the semiconductor substrate, and a conductive layer contacting a top surface of the impurity region and at least a side surface of the impurity region.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/967,089filed on Dec. 14, 2010, the content of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method offabricating the same.

Priority is claimed on Japanese Patent Application No. 2009-288045, Dec.18, 2009, the content of which is incorporated herein by reference.

2. Description of the Related Art

In recent years, the miniaturization of dynamic random access memory(DRAM) cells has necessitated a reduction in gate length of an accesstransistor (hereinafter, referred to as a “cell transistor”) of a cellarray. However, as the gate length of the cell transistor decreases, ashort channel effect of the cell transistor increases. Thus, thethreshold voltage Vt of the cell transistor is reduced due to anincrease in subthreshold current. Also, when the concentration of asubstrate is increased to suppress a drop in threshold voltage Vt,junction leakage increases. As a result, deterioration of refreshcharacteristics of a DRAM may occur.

Japanese Unexamined Patent Application, First Publications, Nos.JP-A-2006-339476 and JP-A-2007-081095 disclose a trench-gate transistor(also referred to as a “recess channel transistor”) in which a gateelectrode is buried in a trench formed in a silicon substrate. Since itis possible to sufficiently ensure an effective channel length, which isa gate length, of the trench-gate transistor, even a fine DRAM with aminimum processing dimension of about 60 nm or less may be realized.

SUMMARY

In one embodiment, a semiconductor device may include, but is notlimited to, a semiconductor substrate, an impurity region in thesemiconductor substrate, and a conductive layer contacting a top surfaceof the impurity region and at least a side surface of the impurityregion.

In another embodiment, a semiconductor device may include, but is notlimited to, a semiconductor substrate having a groove, an impurityregion in the groove, and a conductive layer in contact with theimpurity region. A bottom of the groove is lower than a top of theimpurity region. The bottom of the groove is adjacent to the sidesurface of the impurity region.

In still another embodiment, a semiconductor device may include, but isnot limited to, a semiconductor substrate having a groove and aconductive layer in the groove. A bottom of a first portion of thegroove is higher than a bottom of a second portion of the groove. Aportion of the semiconductor substrate under the first portion includesan impurity. The conductive layer covers the portion of thesemiconductor substrate under the first portion and at least a portionof the semiconductor substrate under the second portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention will be moreapparent from the following description of certain preferred embodimentstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a fragmentary plan view illustrating a memory cell including asemiconductor device in accordance with one embodiment of the presentinvention;

FIG. 2A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in the semiconductordevice of FIG. 1;

FIG. 2B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in the semiconductordevice of FIG. 1;

FIG. 3A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory in a step involved in amethod of forming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 3B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory in a step involved in amethod of forming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 4A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 3A and 3B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 4B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 3A and 3B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 5A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 4A and 4B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 5B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 4A and 4B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 6A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 5A and 5B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 6B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 5A and 5B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 7A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 6A and 6B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 7B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 6A and 6B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 8A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 7A and 7B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 8B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 7A and 7B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 9A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 8A and 8B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 9B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 8A and 8B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 10A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 9A and 9B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 10B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 9A and 9B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 11A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 10A and 10B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 11B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 10A and 10B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 12A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 11A and 11B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 12B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 11A and 11B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 13A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 12A and 12B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 13B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 12A and 12B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 14A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 13A and 13B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 14B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 13A and 13B involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 15A is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIGS. 14A and 14Binvolved in the method of forming the semiconductor device of FIGS. 1,2A and 2B;

FIG. 15B is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIG. 15A involved inthe method of forming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 15C is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIG. 15B, involved inthe method of forming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 15D is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIGS. 14A and 14B,involved in the method of forming the semiconductor device of FIGS. 1,2A and 2B;

FIG. 15E is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIG. 15D, involved inthe method of forming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 15F is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIG. 15E, involved inthe method of forming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 16A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 14A and 14B involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 16B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 14A and 14B involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 17A is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIGS. 15A and 15B,involved in the method of forming the semiconductor device of FIGS. 1,2A and 2B;

FIG. 17B is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIG. 17A, involved inthe method of forming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 17C is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIG. 17B, involved inthe method of forming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 17D is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIGS. 15A and 15B,involved in the method of forming the semiconductor device of FIGS. 1,2A and 2B;

FIG. 17E is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIG. 17D, involved inthe method of forming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 17F is a fragmentary cross sectional elevation view, a memory cellin a step, subsequent to the step of FIG. 17E, involved in the method offorming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 18A is a fragmentary cross sectional elevation view, a memory cellin a step, subsequent to the step of FIG. 17C, involved in the method offorming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 18B is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIG. 117D, involved inthe method of forming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 18C is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIG. 18B, involved inthe method of forming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 18D is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIG. 18A, involved inthe method of forming the semiconductor device of FIGS. 1, 2A and 2B;

FIG. 19 is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIGS. 18A and 18B,involved in the method of forming the semiconductor device of FIGS. 1,2A and 2B;

FIG. 20A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 16A and 16B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 20B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 16A and 16B, subsequent to the step of FIGS. 19A and19B, involved in the method of forming the semiconductor device of FIGS.1, 2A and 2B;

FIG. 21A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 20A and 20B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 21B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 20A and 20B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 22A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 21A and 21B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 22B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 21A and 21B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 23A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 22A and 22B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 23B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 22A and 22B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 24A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 23A and 23B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 24B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 23A and 23B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 25A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 24A and 24B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 25B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 24A and 24B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 26A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 25A and 25B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 26B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 25A and 25B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 27A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 26A and 26B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 27B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell in a step, subsequent tothe step of FIGS. 26A and 26B, involved in the method of forming thesemiconductor device of FIGS. 1, 2A and 2B;

FIG. 28A a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell in a step, illustratinganother embodiment of the present invention;

FIG. 28B a fragmentary cross sectional elevation view, taken along anB-B′ line of FIG. 1, illustrating a memory cell in a step, illustratinganother embodiment of the present invention;

FIG. 29 a fragmentary plan view integrally illustrating a memory cellincluding a semiconductor device in accordance with one embodiment ofthe present invention;

FIG. 30A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell including asemiconductor device in accordance with another embodiment of thepresent invention;

FIG. 30B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell including asemiconductor device in accordance with another embodiment of thepresent invention;

FIG. 31A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell including asemiconductor device in accordance with another embodiment of thepresent invention;

FIG. 31B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell including asemiconductor device in accordance with another embodiment of thepresent invention;

FIG. 32A is a fragmentary cross sectional elevation view, taken along anA-A′ line of FIG. 1, illustrating a memory cell including asemiconductor device in accordance with another embodiment of thepresent invention;

FIG. 32B is a fragmentary cross sectional elevation view, taken along aB-B′ line of FIG. 1, illustrating a memory cell including asemiconductor device in accordance with another embodiment of thepresent invention;

FIG. 33 is a fragmentary cross sectional elevation view illustrating amemory cell including a semiconductor device in accordance with arelated art of the present invention;

FIG. 34A is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIGS. 26A and 26B,involved in the method of forming the semiconductor device of FIGS. 1,2A and 2B;

FIG. 34B is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIGS. 26A and 26B,involved in the method of forming the semiconductor device of FIGS. 1,2A and 2B;

FIG. 34C is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIGS. 26A and 26B,involved in the method of forming the semiconductor device of FIGS. 1,2A and 2B;

FIG. 34D is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIGS. 26A and 26B,involved in the method of forming the semiconductor device of FIGS. 1,2A and 2B;

FIG. 34E is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIGS. 26A and 26B,involved in the method of forming the semiconductor device of FIGS. 1,2A and 2B; and

FIG. 34F is a fragmentary cross sectional elevation view, illustrating amemory cell in a step, subsequent to the step of FIGS. 26A and 26B,involved in the method of forming the semiconductor device of FIGS. 1,2A and 2B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before describing the present invention, the related art will beexplained in detail with reference to drawings, in order to facilitatethe understanding of the present invention.

FIG. 33 is a schematic cross-sectional view showing an example of astructure of a DRAM including a trench-gate cell transistor. In a DRAM200 having the structure shown in FIG. 33, element isolation regions 202are formed in a surface of a P-type silicon substrate 201 and spacedapart from each other from side to side. Gate trenches 204 are formed ina region of the semiconductor substrate 201 interposed between theelement isolation regions 202 and spaced apart from each other in alateral direction of FIG. 33. Gate electrodes 212 are formed to fill thegate trenches 204 through a gate insulating layer 205 formed on innerwalls of the gate trenches 204 between the gate electrodes 212 and thegate trenches 204.

The gate electrodes 212 fill the gate trenches 204 and simultaneouslyprotrude upward from the silicon substrate 201. In the above-describedstructure, each of the gate electrodes 212 has a triple structureobtained by sequentially stacking a polysilicon (poly-Si) layer 206, ametal layer 210 having a high-melting point, and a gate cap insulatinglayer 211. Portions protruding from the gate trenches 204 are covered bya first interlayer insulating layer 214A formed on the semiconductorsubstrate 201.

A high-concentration P-type diffusion layer 208 and a high-concentrationN-type diffusion layer 209 are stacked on the surface of the siliconsubstrate 201 between the gate electrodes 212 shown in FIG. 33, whilelow-concentration N-type diffusion layers 213 are simultaneously formedin regions outside the gate electrodes 212. A contact plug 215A, whichis a bit line contact, functioning as a vertical electrical conductionpath is formed in the first interlayer insulating layer 214A formed overthe high-concentration N-type diffusion layer 209. Contact plugs 215Bfunctioning as vertical electrical conduction paths are formed in thefirst interlayer insulating layer 214A formed over the low-concentrationN-type diffusion layers 213.

Next, a second interlayer insulating layer 214B is formed over the firstinterlayer insulating layer 214A. A bit line 216 is formed in the secondinterlayer insulating layer 214B formed over the contact plug 215A, andsecond contact plugs 215C functioning as vertical electrical conductionpaths are simultaneously formed in the second interlayer insulatinglayer 214B formed over the contact plugs 215B.

Furthermore, a third interlayer insulating layer 214C is formed over thesecond interlayer insulating layer 214B. Cell capacitors 217 are formedin the third interlayer insulating layer 214 formed on the secondcontact plugs 215C. A fourth interlayer insulating layer 214D is formedover the third interlayer insulating layer 214C. Upper electrodes 217Aof the cell capacitors 217 are connected to an upper interconnection 218via a third contact plug 215D formed in the fourth interlayer insulatinglayer 214D. Thus, the DRAM 200 having the schematic structure shown inFIG. 33 is constructed.

In the structure of the DRAM 200 including the trench-gate celltransistor shown in FIG. 33, since the gate electrodes 212 areconfigured to protrude upward from the silicon substrate 201 to thefirst interlayer insulating layer 214A, the contact plug 215A, which isa bit line contact, should be necessarily formed between gate linesconnected to the gate electrodes 212. However, since the intervalbetween the gate lines is extremely small, processing of the contactplug 215A is difficult.

In order to avoid the above-described problems in the trench-gate celltransistor, the present inventor consider it possible to adopt a buriedstructure shown in FIGS. 34A through 34F.

In the buried structure shown in FIGS. 34A through 34F, a plurality oftrenches 231 are formed at predetermined intervals in a lateraldirection of FIG. 34A in a surface of a semiconductor substrate 230 asshown in FIG. 34A. A gate electrode 232 is buried in each of thetrenches 231 with a gate insulating layer 233 interposed therebetween,and a buried insulating layer 235 is buried over the gate electrode 232with a liner layer 234 interposed therebetween. Also, referring to FIG.34A, an impurity diffusion layer 230A is formed using an ionimplantation process in a portion of the surface of the semiconductorsubstrate 230 between the trenches 231 disposed adjacent to each otherin a lateral direction.

To form a gate electrode in the buried structure, an interlayerinsulating layer 236 is stacked on the semiconductor substrate 230, anda contact hole 230B is formed using photolithography and etchingtechniques to be connected to the impurity diffusion layer 230A.Thereafter, a polysilicon layer 237 is formed and then patterned usingphotolithography and etching techniques in the shape of a bit linecontaining a gate electrode so that a bit line containing a desired gateelectrode can be formed. Also, at this time, before the patterningprocess, an impurity ion, such as phosphorus (P), may be introduced intothe polysilicon layer 237 as shown in FIG. 34B.

Furthermore, according to processes shown in FIGS. 34A through 34C, inconsideration of a transistor structure that will be formed in aperipheral circuit region of the DRAM, non-doped polysilicon layers 253and 254 may be stacked in a first forming region 251 and a secondforming region 252 shown in FIG. 34D. The first formation region 251 isan NMOS transistor forming region or the like in a peripheral circuitregion 250 of the semiconductor substrate 230. The second formationregion 252 is a PMOS transistor forming region or the like in aperipheral circuit region 250 of the semiconductor substrate 230. Thus,an NMOS transistor or a PMOS transistor may be formed over an elementisolation region 256. In this case, as shown in FIG. 34E, the secondforming region 252 may be covered by a photoresist layer 257 and anN-type impurity ion, such as phosphorus (P), may be introduced into thefirst forming region 251. Next, as shown in FIG. 34F, the first formingregion 251 may be covered by a photoresist layer 258, and a P-typeimpurity ion, such as boron (B) ion, may be introduced into the secondforming region 252. Thus, the NMOS transistor and the PMOS transistorare normally formed in a peripheral-transistor forming region.

However, even if phosphorus is introduced into the polysilicon layer 237to be currently applied, since the polysilicon layer 237 has a lowphosphorus concentration, it is impossible to reduce a contactresistance between a bit line formed by the polysilicon layer 237 andthe impurity diffusion layer 230A of the semiconductor substrate 230.

Embodiments of the invention will be now described herein with referenceto illustrative embodiments. Those skilled in the art will recognizethat many alternative embodiments can be accomplished using the teachingof the embodiments of the present invention and that the invention isnot limited to the embodiments illustrated for explanatory purpose.

In one embodiment, a semiconductor device may include, but is notlimited to, a semiconductor substrate, an impurity region in thesemiconductor substrate, and a conductive layer contacting a top surfaceof the impurity region and at least a side surface of the impurityregion.

In some cases, the semiconductor device may include, but is not limitedto, the conductive layer including a side contact portion contacting theside surface of the impurity region. The side contact portion is lowerthan the top surface of the impurity region.

In some cases, the semiconductor device may further include, but is notlimited to, the conductive layer including a lower layer of a dopedpolysilicon.

In some cases, the semiconductor device may further includes include,but is not limited to, a metal layer over the conductive layer.

In some cases, the semiconductor device may include, but is not limitedto, the conductive layer being a wiring layer. The impurity region isone of a source region and a drain region of a transistor.

In some cases, the semiconductor device may further include, but is notlimited to, a pair of oxide layers. The impurity region is interposedbetween the pair of oxide layers.

In another embodiment, a semiconductor device may include, but is notlimited to, a semiconductor substrate having a groove, an impurityregion in the groove, and a conductive layer in contact with theimpurity region. A bottom of the groove is lower than a top of theimpurity region. The bottom of the groove is adjacent to the sidesurface of the impurity region.

In some cases, the semiconductor device may further include, but is notlimited to, the conductive layer including a side contact portioncontacting the side surface of the impurity region. The side contactportion is lower than the top surface of the impurity region.

In some cases, the semiconductor device may include, but is not limitedto, the conductive layer including a lower layer of a doped polysilicon.

In some cases, the semiconductor device may further include, but is notlimited to, a metal layer over the conductive layer.

In some cases, the semiconductor device may include, but is not limitedto, the conductive layer being a wiring layer. The impurity region isone of a source region and a drain region of a transistor.

In some cases, the semiconductor device may further include, but is notlimited to, a pair of oxide layers. The impurity region is interposedbetween the pair of oxide layers.

In some cases, the semiconductor device may include, but is not limitedto, the conductive layer contacting the bottom of the groove.

In still another embodiment, a semiconductor device may include, but isnot limited to, a semiconductor substrate having a groove and aconductive layer in the groove. A bottom of a first portion of thegroove is higher than a bottom of a second portion of the groove. Aportion of the semiconductor substrate under the first portion includesan impurity. The conductive layer covers the portion of thesemiconductor substrate under the first portion and at least a portionof the semiconductor substrate under the second portion.

In some cases, the semiconductor device may further include, but is notlimited to, the conductive layer including a side contact portioncontacting the side surface of the impurity region. The side contactportion is lower than the top surface of the impurity region.

In some cases, the semiconductor device may include, but is not limitedto, the conductive layer including a lower layer of a doped polysilicon.

In some cases, the semiconductor device may further include, but is notlimited to, a metal layer over the conductive layer.

In some cases, the semiconductor device may include, but is not limitedto, the conductive layer being a wiring layer. The impurity region isone of a source region and a drain region of a transistor.

In some cases, the semiconductor device may further include, but is notlimited to, a pair of oxide layers. The impurity region is interposedbetween the pair of oxide layers.

In some cases, the semiconductor device may include, but is not limitedto, the conductive layer contacting the bottom of the groove.

In still another embodiment, a method for forming a semiconductor devicemay include, but is not limited to, the following processes. Aninsulating layer is formed over a semiconductor substrate. A groove inthe insulating layer is formed to expose a portion of the semiconductorsubstrate. A first impurity is introduced into the portion of thesemiconductor substrate. A polysilicon layer which may include a secondimpurity is formed, the polysilicon layer contacting the portion of thesemiconductor substrate. The second impurity is introduced into thepolysilicon layer. The polysilicon layer is patterned to form a wiringconnected to the portion of the semiconductor substrate.

In some cases, the method for forming a semiconductor device mayinclude, but is not limited to, the following processes. The portion ofthe semiconductor substrate has a first portion and the second portionbelow the first portion. The first impurity is introduced into the firstportion at a high concentration. The first impurity is introduced intothe second portion at a low concentration.

In some cases, the method for forming the semiconductor device mayinclude, but is not limited to, the following processes. The wiring isformed by laminating the polysilicon layer and a metal layer.

In still another embodiment, a method for forming a semiconductor devicemay include, but is not limited to, the following processes. Asemiconductor substrate which includes a cell transistor region and aperipheral circuit region is prepared. An insulating film is formed overthe cell transistor region. A groove is formed in the insulating layerto expose a portion of the semiconductor substrate in the celltransistor region. First impurity is introduced into the portion of thesemiconductor substrate in the cell transistor region. A firstpolysilicon layer is formed in the peripheral circuit region. A secondpolysilicon layer which may include second impurity is formed in thecell transistor region and the peripheral circuit region, thepolysilicon layer contacting the portion of the semiconductor substrate.The second impurity is introduced into the second polysilicon layer. Thesecond polysilicon layer in the cell transistor region is patterned toform a wiring connected to the portion of the semiconductor substrate.The second polysilicon layer in the peripheral circuit region ispatterned to form a gate electrode of a transistor.

Hereinafter, in one embodiment, a DRAM (Dynamic Random Access Memory) asthe semiconductor device will be described. In the drawings used for thefollowing description, to facilitate understanding of the embodiments,illustrations are partially enlarged and shown, and the sizes and ratiosof constituent elements are not limited to being the same as the actualdimensions. Materials, sizes, and the like exemplified in the followingdescription are just examples, and the invention is not limited theretoand may be appropriately modified within the scope which does notdeviate from the embodiments.

<Structure of Semiconductor Memory Device>

FIG. 1 is a plan view of some elements of a cell structure of asemiconductor memory device. FIGS. 2A and 2B are partial cross-sectionalviews of the semiconductor memory device. FIG. 2A is a cross-sectionalview taken along line A-A′ of FIG. 1, and FIG. 2B is a cross-sectionalview taken along line B-B′ of FIG. 1.

A semiconductor memory device 1 of an embodiment of the presentinvention has a cell-transistor forming region 2 and a cell-capacitorforming region 3 shown in the cross-sectional views of FIGS. 2A and 2B.A semiconductor substrate 5 may be a conductive silicon substrate.

In the cell-transistor forming region 2, a plurality of strip-shapedactive regions K are formed in one surface of the semiconductorsubstrate 5 in a direction inclined at a predetermined angle withrespect to an X direction of FIG. 1, that is, in a direction inclined ina lateral direction of FIG. 1, and spaced by a predetermined distanceapart from one another in a Y direction. In addition, to define theactive regions K, a plurality of element isolation trenches 4 having asectional shape shown in FIG. 2A are formed in a direction inclined at apredetermined angle with the X direction of FIG. 1. The plurality ofelement isolation trenches 4 are spaced by a predetermined distanceapart from one another in the Y direction of FIGS. 1 and 2A. As shown inFIG. 2A, an inner insulating layer 4A may include a silicon oxide layeron inner surfaces of the element isolation trenches 4. An elementisolation insulating layer 6 may include a silicon nitride layer insidethe inner insulating layer 4A to fill the element isolation trenches 4,thereby forming element isolation regions (shallow trench isolation(STI) regions).

Furthermore, although the arrangement of the active regions K in aplanar shape as shown in FIG. 1 is unique to the one embodiment of thepresent invention, the shape and alignment direction of the activeregions K may not be particularly limited. The shape of the activeregions K shown in FIG. 1 may naturally be the shape of active regionsapplied to other typical transistors and is not limited to the shape ofthe one embodiment of the present invention.

Also, as shown in FIG. 2B, a plurality of gate-electrode trenches 7extend in the Y direction of FIG. 1 and are spaced a predetermineddistance apart from each other in the X direction of FIGS. 1 and 2B. Agate insulating layer 7A may include a silicon oxide layer on innersurfaces of the gate-electrode trenches 7. A buried word line 9 mayinclude a metal having a high melting point, such as tungsten (W),inside the gate insulating layer 7A with an inner surface layer 8 whichmay include titanium nitride interposed therebetween. A buriedinsulating layer 11 is formed over the buried word line 9 to fill thegate-electrode trenches 7 with a liner layer 10 interposed therebetween.

In FIG. 1, the gate-electrode trenches 7 in which the buried word lines9 are formed include two kinds of trenches. One of trenches is formed asa channel of a trench-gate transistor in a portion overlapping theactive region K. The other of trenches is formed as a trench formed inthe STI region adjacent to the active region K to a smaller depth thanthe trench formed in the active region K. The buried word line 9 isformed as a single continuous interconnection with a planar top surfaceto fill two kinds of trenches with different depths.

Furthermore, in the one embodiment of the present invention, the gateinsulating layer 7A and the liner layer 10 are formed such that top endedges of the gate insulating layer 7A and the liner layer 10 reachopenings of the gate-electrode trenches 7. The buried insulating layer11 is formed to fill a convex portion of the liner layer 10 formed in anopening of the gate insulating layer 7A. Thus, the buried insulatinglayer 11, the gate insulating layer 7A, and the liner layer 10 arestacked such that a top surface of the buried insulating layer 1, a topend edge of the gate insulating layer 7A, and a top end edge of theliner layer 10 substantially form one plane.

In the one embodiment of the present invention, the buried insulatinglayer 11 may be a solid layer obtained by coating a silicon oxide layeror a spin-on-dielectrics (SOD), which is an insulating coating layerwhich may include polysilazane, using a chemical vapor deposition (CVD)method and annealing the coated layer at a high temperature in amoisture-containing atmosphere.

As shown in FIG. 2A, a channel trench 12 is formed to a smaller depththan the element isolation trench 4 in a region between the elementisolation trenches 4 adjacent to each other in the Y direction. The gateinsulating layer 7A may include a silicon oxide layer over innersurfaces of the channel trench 12 and top surface of the elementisolation trench 4 disposed adjacent to the channel trench 12. Anelement isolation buried wiring 13 is formed over the gate insulatinglayer 7A with the inner surface layer 8 which may include titaniumnitride interposed therebetween. The liner layer 10 and the buriedinsulating layer 11 are stacked on the buried wiring 13. The liner layer10 and the buried insulating layer 11 shown in FIG. 2A are the same asthe liner layer 10 and the buried insulating layer 11 formed over theburied word line 9 shown in FIG. 2B, which are fabricated during by thefollowing method.

Also, the element isolation buried wiring 13 is formed while the buriedword line 9 is formed. The element isolation buried wiring 13 functionsto electrically isolate source and drain regions, that is, impuritydiffusion regions formed on both sides of the element isolation buriedline 13 shown in FIG. 1, which constitute respective adjacenttransistors in an active region formed in a line shape. Conventionally,an active region is formed as an isolated pattern surrounded by a buriedelement isolation region formed using an insulating layer. Accordingly,source and drain regions cannot be formed in a desired shape in an endportion of the active region due to the resolution limit of alithography process. However, the construction of the one embodiment ofthe present invention may avoid the above-described problem because anactive region may be formed in a line-shaped pattern.

As shown in FIGS. 1 and 2B, a plurality of buried word lines 9 extend inthe Y direction and are spaced apart from one another in the Xdirection. However, in the structure of the one embodiment of thepresent invention, as shown in FIG. 2B, two buried word lines 9 and oneelement isolation buried wiring 13 are alternately arranged in thisorder in the X direction.

Also, as shown in FIG. 1, a bit line 15, which will be described indetail later, is disposed in a direction perpendicular to a direction inwhich the buried word line 9 and the buried line 13 are arranged.Accordingly, the active regions K having a strip-type plane shape areformed in the surface of the semiconductor substrate 5 to be inclined ata predetermined angle with a direction in which each of the buried wordwirings 9 and each of the bit lines 15 extend. Since the active regionsK are formed in the surface of the semiconductor substrate 5, a bit lineconnection region 16 is defined in a portion of the active region Kdisposed below each of the bit lines 15. Also, when an interconnectionstructure is viewed from the plan view as shown in FIG. 1, a capacitorcontact plug forming region 17 is defined in a portion where the activeregion K exists, in a region between the buried word line 9 and theelement isolation buried wiring 13 adjacent to the buried word line 9 inthe X direction and between the bit lines 15 and 15 adjacent to anotherbit line in the Y direction.

Accordingly, when the interconnection structures is viewed from the planview, as shown in FIG. 1, the bit lines 15 are approximately orthogonalto the buried word line 9 and the element isolation buried line 13.Simultaneously, the strip-shaped active regions K are disposed at anangle with the bit lines 15. Bit line connection regions 16 are formedin portions of the active regions K corresponding to regions betweenadjacent buried word lines 9. The capacitor contact plug forming region17 is defined in a region between the buried word line 9 and the elementisolation region 13 and between adjacent bit lines 15. Also, a capacitorcontact pad 18 that will be described later is formed in a zigzagpattern with respect to the capacitor contact plug forming region 17 inthe Y direction of FIG. 1. Although the capacitor contact pads 18 aredisposed in the X direction of FIG. 1 between the bit lines 15 adjacentto each other in the Y direction, the capacitor contact pads 18 arerepetitively disposed zigzag in several positions in the Y direction.For example, the center of one capacitor contact pad 18 may be disposedover the buried word line 9 in the Y direction and the center of anothercapacitor contact pad 18 may be disposed over one side of the buriedword line 9. In other words, the capacitor contact pads 18 are disposedzigzag in the Y direction.

Next, in the one embodiment of the present invention, the capacitorcontact plug 19 formed in the capacitor contact plug forming region 17is formed in a rectangular shape as shown in FIG. 1. However, a portionof the capacitor contact plug 19 is disposed on each of the buried wordlines 9, while the remaining portion of the capacitor contact plug 19 isdisposed to be located in a region between the adjacent bit lines 15 andover a region between the buried word line 9 and the element isolationburied line 13 so that each of the capacitor contact plugs 19 can beconnected to a capacitor 47 that will be described later.

From the plan view of FIG. 1, the capacitor contact plug forming region17 may cover a portion of the buried word line 9, a portion of the STIregion, and a portion of the active region K. Accordingly, from the planview, the capacitor contact plug 19 is formed to range over the portionof the buried word line 9, the portion of the STI region, and theportion of the active region K.

The cell-transistor forming region 2 will be described again withreference to FIGS. 2A and 2B. As shown in FIG. 2B, a low-concentrationimpurity diffusion layer 21 and a high-concentration impurity diffusionlayer 22 are formed sequentially from a depth direction on the surfaceof the semiconductor substrate 5 located between the buried word lines 9adjacent to each other in the X direction and in a region correspondingto the active region K. A low-concentration impurity diffusion layer 23and a high-concentration impurity diffusion layer 24 are formedsequentially from the depth direction on the surface of thesemiconductor substrate 5 located between the buried word line 9 and theelement isolation buried wiring 13 adjacent in the X direction and in aregion corresponding to the active region K.

Thus, a first interlayer insulating layer 26 is formed to cover theburied insulating layer 11 in the region shown in FIG. 2A. The firstinterlayer insulating layer 26 is formed over the semiconductorsubstrate 5 in the region shown in FIG. 2B. That is, the firstinterlayer insulating layer 26 is formed to cover the cover thehigh-concentration impurity diffusion layers 22 and 24 and thegate-electrode trench 7 in which the buried word line 9, the liner layer10, and the buried insulating layer 11 are formed.

A contact hole 28 is formed in a region of the first interlayerinsulating layer 26 between the gate-electrode trenches 7 adjacent toeach other in the X direction of FIG. 2B. As shown in FIG. 1, the bitlines 15 are formed over the first interlayer insulating layer 26 andextend in a direction perpendicular to the buried word line 9. In thiscase, the bit lines 15 are disposed in portion of the contact hole 28,extend to lower portion of the contact hole 28. Further, the bit lines15 are connected to the high-concentration impurity layer 22 formedunder the respective contact holes 28. Accordingly, a portion includingthe bit line 15 of a region in which the contact hole 28 is formed,i.e., a region having the high-concentration impurity diffusion layer 22therebeneath becomes the bit line connection region 16.

The bit line 15 has a triple structure including a lower conductivelayer 30 which may include polysilicon, a metal layer 31 which mayinclude a metal having a high melting point, such as tungsten (W), andan upper insulating layer 32 which may include silicon nitride. Aninsulating layer 33, such as a silicon nitride layer, and a liner layer34 are respectively formed on both sides of a widthwise direction of thebit line 15 shown in FIG. 2B and on the first interlayer insulatinglayer 26 shown in FIG. 2A.

More specifically, as will be described in the following fabricationmethod, the lower conductive layer 30 is an introduced polysilicon layerformed by further implanting impurity ion, such as phosphorus (P) ion,into polysilicon doped with impurity, such as phosphorus ion. Also, sidecontact portions 30 a are formed on both ends of the lower conductivelayer 30 disposed on both sides of a widthwise direction of the bit line15 and protrude in a depth direction of the semiconductor substrate 50.Since the side contact portions 30 a are formed on both sides of thelower conductive layer 30, the bit line 30 is connected to thehigh-concentration impurity diffusion layer 22 of the semiconductorsubstrate 5 to surround the high-concentration impurity diffusion layer22, thereby contributing to reducing a contact resistance.

A capacitor contact opening 36, which has a rectangular shape whenviewed from a plan view, is formed in a region between the bit lines 15adjacent to each other in the Y direction of FIG. 1. The capacitorcontact opening 36 is over a region between an upper region of theburied word line 9 and the element isolation buried wiring 13 disposedadjacent thereto. A capacitor contact plug 19 is formed within thecapacitor contact opening 36 and surrounded by sidewalls 37 which mayinclude a silicon nitride layer. Accordingly, a portion where thecapacitor contact opening 36 is formed corresponds to the capacitorcontact plug forming region 17. As shown in FIG. 2B, the capacitorcontact plug 19 has a triple layer structure including a lowerconductive layer 40 which may include polysilicon, a silicide layer 41which may include CoSi, and a metal layer 42 which may include W. Also,the bit line 15 and the capacitor contact plug 19 are formed on thesemiconductor substrate 5 at the same level. Also, a buried insulatinglayer 43 is formed in the remaining region of the bit line 15 and thecapacitor contact plug 19 at the same level as the bit line 15 and thecapacitor contact plug 19.

Next, in the capacitor forming region 3 shown in FIGS. 2A and 2B, eachof the capacitor contact pads 18 having a circular shape shown in FIG. 1is formed to be zigzag with respect to the capacitor contact plug 19 topartially overlap the capacitor contact plug 19 from a plan view. Eachof the capacitor contact pads 18 is covered by a stopper layer 45, whilea third interlayer insulating layer 46 is simultaneously formed over thestopper 45. A capacitor 47 is formed over each of the capacitor contactpads 18 within the third interlayer insulating layer 46.

The capacitor 47 according to the one embodiment of the presentinvention includes a cup-type lower electrode 47A, a capacitorinsulating layer 47B, an upper electrode 47C, a fourth interlayerinsulating layer 48, an upper metal interconnection 49, and a protectionlayer 54. The cup-type lower electrode 47A is formed over the capacitorcontact pad 18. The capacitor insulating layer 47B is formed to extendfrom the inside of the lower electrode 47A to the third interlayerinsulating layer 46. The upper electrode 47C is formed to bury theinside of the lower electrode 47A within the capacitor insulating layer47B and simultaneously extend to the top surface of the capacitorinsulating layer 47B. The fourth interlayer insulating layer 48 isformed over the upper electrode 47. The upper metal interconnection 49is formed over the fourth interlayer insulating layer 48. The protectionlayer 54 is formed to cover the upper metal interconnection 49 and thefourth interlayer insulating layer 48. In addition, the structure of thecapacitor 47 formed in the capacitor forming region 3 is an example, andother typical capacitors (e.g., crown-type capacitors) applied tosemiconductor memory devices may naturally be employed.

<Method of Fabricating Semiconductor Device>

Next, an example of a method of fabricating the semiconductor deviceshown in FIGS. 1, 2A, and 2B will be described with reference to FIGS.3A through 23B. FIGS. 3A through 23A are cross-sectional views ofportions taken along line A-A′ of FIG. 1, and FIGS. 3B through 23B arecross-sectional views of portions taken along line B-B′ of FIG. 1.

A semiconductor substrate 50, such as a P-type Si substrate, is preparedas shown in FIGS. 3A and 3B. A silicon oxide layer 51 and a siliconnitride (Si₃N₄) layer 54 serving as a mask are sequentially stacked.Also, a semiconductor substrate in which a P-well is previously formedusing an ion implantation process in a region where a transistor is tobe formed may be used as the semiconductor substrate 50.

Next, the silicon oxide layer 51, the silicon nitride layer 52, and thesemiconductor substrate 50 are patterned using photolithography and dryetching techniques, thereby forming element isolation trench 53. Theelement isolation trench is formed in a surface of the silicon substrate50 to define active regions K. From the plan view of the semiconductorsubstrate 50, the element isolation trench 53 is formed as a line-shapedpattern trench extending in a predetermined direction between both sidesof the strip-shaped active region K of FIG. 1. A region corresponding tothe active region K is covered by the silicon nitride layer 52.

Next, as shown in FIGS. 4A and 4B, a silicon oxide layer 55 is formedusing a thermal oxidation method on the surface of the semiconductorsubstrate 50. Afterwards, a silicon nitride layer is deposited to fillthe element isolation trench 53 and then etched back. Thus, the siliconnitride layer is left only in a lower portion of the element isolationtrench 53 and filled up to a slightly lower position than the topsurface of the semiconductor substrate 50. An element isolationinsulating layer 56 having such a thickness is completed as shown inFIGS. 4A and 4B.

Next, a silicon oxide layer 57 is deposited using a CVD process to fillthe inside of the element isolation trench 53. The surface of thesilicon oxide layer 57 is planarized using a chemical mechanicalpolishing (CMP) process as shown in FIGS. 5A and 5B until the siliconnitride layer 52 serving as a mask, which is formed in FIG. 3, isexposed.

Next, the silicon nitride layer 52 serving as the mask and the siliconoxide layer 51 are removed using a wet etching process so that thesurface of the element isolation trench 53 is substantially the samelevel as the surface of the silicon substrate 50. Thus, a line-shapedelement isolation region 58 using an STI structure shown in FIGS. 6A and6B is formed. After the surface of the silicon substrate 50 is exposed,a thermal oxidation process is carried out, thereby forming a siliconoxide layer 60 in the surface of the semiconductor substrate 50.

Subsequently, as shown in FIGS. 6A and 6B, low-concentration N-typeimpurity ion, such as phosphorus ion, are introduced, thereby forming anN-type low-concentration impurity diffusion layer 61. The N-typelow-concentration impurity diffusion layer 61 functions as a portion ofsource and drain (S/D) regions of a recess-type transistor according tothe present invention.

Next, a silicon nitride layer 62 serving as a mask and a carbon layer63, which is an amorphous carbon layer, are sequentially deposited andpatterned to form a gate-electrode trench, which is a trench, as shownin FIGS. 7A and 7B.

Also, as shown in FIGS. 8A and 8B, the semiconductor substrate 50 isetched using a dry etching process, thereby forming trenches 65, whichis a gate-electrode trench. The trench 65 is formed in line-shapedpatterns extending in a predetermined direction, which is the Ydirection of FIG. 1, to intersect the active region K.

At this time, a top surface of the element isolation region 58 disposedwithin the trench 65 is also etched, thereby forming a shallow trench ina lower position than the top surface of the semiconductor substrate 50.Etching conditions are controlled such that a silicon oxide layer isetched at a lower etch rate than the semiconductor substrate 50. Thus,the trench 65 is formed as a continuous trench having a lower portionwith a step difference. That is, the trench 65 is the continuous trenchincluding a deep trench formed by etching the semiconductor substrate 50and a shallow trench formed by etching the element isolation region 58.As a result, as shown in FIGS. 8A and 8B, a thin silicon layer isremained as sidewalls 66 in a lateral surface of the trench 65neighboring the element isolation region 58 and functions as a channelregion of a recess-type cell transistor. By etching silicon of thesemiconductor 50 to a greater depth than the element isolation region(STI) 58, a channel region of a recess channel transistor is formed asshown in FIGS. 8A and 8B.

Next, a gate insulating layer 67 is formed as shown in FIGS. 9A and 9B.A silicon oxide layer formed using a thermal oxidation process may beused as the gate insulating layer 67. Afterwards, an inner surface layer68 which may include titanium nitride (TiN) and a tungsten (W) layer 69are sequentially deposited.

Next, an etch-back process is performed until the inner surface layer 68and the tungsten layer 69 are left in a lower portion of the trench 65.Thus, as shown in FIGS. 10A and 10B, a buried word line 70, whichconstitutes a portion of a gate electrode, and an element isolationburied wiring 73 are formed.

As shown in FIGS. 11A and 11B, a liner layer 71 may include a siliconnitride (Si₃N₄) layer to cover the remaining W layer 69 and an innerwall of the trench 65. The liner layer 71 has a thickness of about 10 nmA buried insulating layer 72 is deposited over the liner layer 71 usinga CVD process or an SOD, which is an insulating coating layer which mayinclude polysilazane.

Next, as shown in FIGS. 12A and 12B, the surface of the buriedinsulating layer 72 is planarized using a CMP process until the linerlayer 71 is exposed. Thereafter, the silicon nitride layer serving as amask and portions of the buried insulating layer 72 and the liner layer71 are removed using an etching process so that the surface of theburied insulating layer 72 can be at about the same level as the siliconsurface of the semiconductor substrate 50. Thus, a buried word line 70and an element isolation buried wiring 73 are formed, and a buriedinsulating layer 74 is formed over the buried word line 70 and theburied line 73.

Next, as shown in FIGS. 13A and 13B, a first interlayer insulating layer75 may include a silicon oxide layer to cover the semiconductorsubstrate 50. Afterwards, a portion of the first interlayer insulatinglayer 75 is removed using photolithography and dry etching techniques,thereby forming a bit contact opening 76. As in the case shown in FIG.1, the bit contact opening 76 is formed in a line-shaped opening patternextending in the same direction as the buried word line 70 (the Ydirection of FIG. 1 or a direction in which the buried word line 70 andthe buried line 73 extend in FIGS. 13A and 13B). Hence, the Si surfaceof the semiconductor substrate 50 is exposed in a portion of the patternof the bit contact opening 76, which intersects the active region K.Thus, the exposed portion is used as a bit line connection region.

After the bit contact opening 76 is formed, N-type impurity ion, such asarsenic (As) ion, is introduced, thereby forming a high-concentrationN-type impurity diffusion layer 77 near the silicon surface of thesemiconductor substrate 50. The high-concentration N-type impuritydiffusion layer 77 functions as source and drain regions of arecess-type cell transistor.

Next, as shown in FIGS. 14A and 14B, a lower conductive layer 78 whichmay include a polysilicon layer containing N-type impurity ion, such asphosphorus ion, a metal layer 79, such as a tungsten layer, and asilicon nitride layer 80 are sequentially deposited over thesemiconductor substrate 50.

Specifically, as shown in FIG. 15A, a contact opening 75A is formed inthe first interlayer insulating layer 75 to reach a portion of anopening of the trench 65 formed by burying adjacent buried word lines 70constituting a portion of a gate electrode. The contact opening 75A isformed to such a width so as to cover the high-concentration N-typeimpurity diffusion layer 77 between the trenches 65 arranged on left orright side with each other in the X direction. Additionally, the contactopening 75A reaches the buried insulating layer 74 formed in openings ofthe trenches 65 arranged on the left or right side with each other inthe X direction.

Also, N-type impurity ion, such as phosphorus ion, are doped onto thesemiconductor substrate 50 and the first interlayer insulating layer 75,thereby forming an impurity-doped polysilicon layer 78A. Thus, N-typeimpurity ion, such as phosphorus ion, is introduced from thesemiconductor substrate 50 into the impurity-doped polysilicon layer78A, so that a high-concentration introduced polysilicon layer 78B canbe obtained.

Next, a state of the peripheral circuit region, which is a MOStransistor region, of the DRAM in addition to the cell transistor regionwill be described with reference to FIGS. 15A through 18D.

Before forming the impurity-doped polysilicon layer 78A as shown in FIG.15A, a non-doped polysilicon layer 300 is formed in a peripheral circuitregion 301 as shown in FIG. 15D. Also, for brevity, an NMOS region and aPMOS region of the peripheral circuit region 301 will be referred to asa first region 302 and a second region 303, respectively. Furthermore,the first and second regions 302 and 303 are electrically isolated fromeach other by an element isolation insulating layer 304 formed in thesemiconductor substrate 50. A gate oxide layer 305 is formed along aregion isolated by the element isolation insulating layer 304 of thesemiconductor substrate 50 and the surface of the semiconductorsubstrate 50 surrounded by the isolated region.

Initially, when the impurity-doped polysilicon layer 78A is formed asshown in FIG. 15A, the impurity-doped polysilicon layer 78A is stackedin the peripheral circuit region 301 as well.

In a case where N-type impurity ion, such as phosphorus ion, isintroduced as shown in FIG. 15B, after the second region 303 is coveredby a photoresist layer 305A, which is a protection layer, in theperipheral circuit region 301, the N-type impurity ion, such as thephosphorus ion, is introduced. Due to the ion implantation process, inthe first region 302, the impurity-doped polysilicon layer 78A and theunderlying non-doped polysilicon layer 300 are changed into ahigh-concentration polysilicon diffusion layer 306 containing N-typeimpurity ion.

Continuously, as shown in FIGS. 15C and 15F, after both the celltransistor region and the first region 302 are covered by a photoresistlayer 307, which is a protection layer, P-type ion, such as boron (B)ion, is introduced to the second region 303. As a result, a polysilicondiffusion layer 308 containing high-concentration P-type impurity ion isformed in the impurity-doped polysilicon layer 78B and the underlyingnon-doped polysilicon layer 300 formed in the second region 303.

Furthermore, the non-doped polysilicon layer 300 is formed in thevicinity of the gate oxide layer 305 in the second region 303 shown inFIG. 15E. Therefore, even if the N-type impurity-doped polysilicon layer78A is formed over the non-doped polysilicon layer 300, as shown in FIG.15F, an implantation of P-type ion such as boron ion may be carried outand forming a PMOS transistor in the second region 303 can beaccomplished.

As shown in FIGS. 15D through 15F, the non-doped polysilicon layer 300and the impurity-doped polysilicon layer 78A are used, and an ionimplantation is separately performed using photoresist layers 305A and307. Accordingly, formation of a layer in the cell transistor region isperformed while PMOS and NMOS transistors in the peripheral circuitregion 301 are separately formed.

Next, in the cell transistor region, as shown in FIGS. 16A and 16B, astacked layer of the introduced polysilicon layer 78B, the metal layer79, and the silicon nitride layer 80 may be patterned in a line shape,thereby forming a bit line 81.

In the structure of the one embodiment of the present invention, sincethe impurity-doped polysilicon layer 78A is applied to the cell region,the bit line 81 may be connected in a low-resistance state to thehigh-concentration impurity diffusion layer 77 using the impurity-dopedpolysilicon layer 78A. Furthermore, since the impurity-doped polysiliconlayer 78A is used as the same introduced polysilicon layer 78B asdescribed above, the bit line 81 may be connected to thehigh-concentration impurity diffusion layer 77 by the introducedpolysilicon layer 78B. Also, impurity ion may further remain inhigh-concentration in a contact portion. As a result, the bit line 81may be connected to the high-concentration impurity diffusion layer 77in a much lower resistance state.

The bit line 81 is formed in a pattern that extends in a direction,which is the X direction used in the description of the structure ofFIG. 1, intersecting the buried word line 70. In addition, although thebit line 81 has a straight line shape disposed at right angles with theburied word line 70 as in the structure shown in FIG. 1, the bit line 81may be partially curved and have a bent-line or wave-like shape. Thelower conductive layer 78 disposed under the bit line 81 is connected tothe high-concentration N-type impurity diffusion layer 77, which is oneof source and drain regions, formed in the surface of the semiconductorsubstrate 50. The connecting region is a surface of the semiconductorsubstrate 50 exposed by the bit contact opening 76. The semiconductorsubstrate 50 may include silicon.

In addition, side contact portions 78 a are formed on both sides of awidthwise direction of the lower conductive layer 78 that constitutelower portions of the bit lines 81. As shown in FIGS. 13A and 13B, whenthe bit contact opening 76 is formed using an etching process, the sidecontact portions 78 a may be formed by partially etching the buriedinsulating layer 74 and the gate insulating layer 67 disposed on bothedges of a widthwise direction of the bit contact opening 76.

Here, the high-concentration impurity diffusion layer 77 is interposedbetween the gate insulating layers 67. A contact area between the lowerconductive layer 78 and the high-concentration impurity diffusion layer77 formed in the surface of the semiconductor substrate 50 is increasedsince the lower conductive layer 78 contacts a top surface of thehigh-concentration impurity diffusion layer 77 and at least side surfaceof the high-concentration impurity diffusion layer 77. The increasedcontact area is advantageous to connecting the bit line 81 and thehigh-concentration impurity diffusion layer 77, thus contributing toreduction of a connection resistance.

In other words, the semiconductor substrate 50 has a groove. Thehigh-concentration impurity diffusion layer 77 is formed in the groove.A bottom of the groove is lower than a top of the high-concentrationimpurity diffusion layer 77. The bottom of the groove is adjacent to theside surface of the high-concentration impurity diffusion layer 77. Thelower conductive layer 78 contacts the bottom of the groove.

Also, the lower conductive layer 78 may be formed in the groove. Abottom of a first portion of the groove is higher than a bottom of asecond portion of the groove. A portion of the semiconductor substrateunder the first portion includes an impurity. The lower conductive layer78 covers the portion of the semiconductor substrate 50 under the firstportion and at least a portion of the semiconductor substrate 50 underthe second portion. The lower conductive layer 78 may contact the bottomof the groove.

Here, the lower conductive layer 78 has a side contact portioncontacting the side surface of the impurity region. The side contactportion is lower than the top surface of the high-concentration impuritydiffusion layer 77. Additionally, the high-concentration impuritydiffusion layer 77 is interposed between the gate insulating layer 67.

Next, as shown in FIGS. 15A and 15B, a stacked layer of the dopedpolysilicon layer 78B, the metal layer 79, and the silicon nitride layer80 is patterned in a line shape to form the bit line 81. As shown inFIGS. 17A through 18D, a MOS transistor is formed in the peripheralcircuit region 301 as well.

The metal layer 79 and the silicon nitride layer 80 are formed over theintroduced polysilicon layer 78B as shown in FIG. 17A, as well as in theperipheral circuit region 301 shown in FIG. 17D. Also, while the bitline 81 is patterned as shown in FIG. 17B, the high-concentrationpolysilicon diffusion layer 306 containing N-type impurity ion and thehigh-concentration polysilicon diffusion layer 308 containing P-typeimpurity ion may be patterned as shown in FIG. 17E. The gate electrodes310 and 311 are formed in the first and second regions 302 and 303,respectively. Next, the entire cell transistor region and the secondregion 303 of the peripheral circuit region are covered by a photoresistlayer 312 as shown in FIGS. 17C and 17F. Impurity ion, such as arsenic(As) ion, is introduced into the vicinity of the gate electrode 310 ofthe first region 302 as shown in FIG. 17F, thereby forming impuritydiffusion layers 313 and 314 in the surface of the semiconductorsubstrate 50 on both sides of the gate electrode 310.

Next, the photoresist layer 312 is removed. The cell transistor regionand the first region 302 are covered by a photoresist layer 315 as shownin FIGS. 18A and 18B. As shown in FIG. 18B, impurity ion, such as boronfluoride (BF₂) ion, may be introduced into the vicinity of the gateelectrode 311 of the exposed second region 303. Impurity diffusionlayers 316 and 317 are formed in the surface of the semiconductorsubstrate 50 on both sides of the gate electrode 311 for source anddrain regions.

In the above-described process, an NMOS transistor 318 and a PMOStransistor 319 may be formed in the peripheral circuit region 301.Subsequently, as shown in FIG. 18D, the following fabrication process isperformed. An interlayer insulating layer 320 is formed. A contactopening 321 is formed in the interlayer insulating layer 320. Contactplugs 322 and 323 are formed. Fabrication of basic components of thetransistors in the peripheral circuit region is accomplished as shown inFIG. 19.

In the cell transistor region, as shown in FIGS. 20A and 20B, after asilicon nitride layer 82 is formed to cover lateral surfaces of the bitline 81, a liner layer 83 may include a silicon nitride layer to cover atop surface of the silicon nitride layer 82.

Furthermore, as described above, the stack layer for the bit line 81 mayfunction also as the gate electrodes 310 and 311 of the MOS transistorin the peripheral circuit of the semiconductor memory device. Thesilicon nitride layer 82 formed to cover the lateral surfaces of the bitlines 81 may be used as portions of sidewalls of the gate electrodes 310and 311 in the peripheral circuit region However, a description ofsidewalls is omitted from the description presented with reference toFIGS. 17A through 18D.

Next, a SOD layer, which is an insulating coating layer which mayinclude polysilazane, is formed to fill space portions 81A between thebit lines 81 shown in FIGS. 20A and 20B. An annealing process isperformed at a high temperature in a moisture (H₂O) atmosphere so thatthe SOD layer can be reformed into a solid deposition layer 85. Theresultant structure is planarized using a CMP process until the surfaceof the liner layer 83 is exposed. Afterwards, as shown in FIGS. 21A and21B, a second interlayer insulating layer 86 may include a silicon oxidelayer using a CVD process to cover the surface of the deposition layer85.

Next, as shown in FIGS. 22A and 22B, a capacitor contact opening 87 isformed using photolithography and dry etching techniques. In the case ofthe structure described above with reference to FIG. 1, the capacitorcontact opening 87 is formed in a position corresponding to thecapacitor contact plug forming region 17. Here, a self-aligned contact(SAC) process may be performed using the silicon nitride layer 82 andthe liner layer 83 formed on lateral surfaces of the bit lines 81 assidewalls, thereby forming the capacitor contact opening 87.

The surface of the semiconductor substrate 50 is exposed in a portionwhere the capacitor contact opening 87 intersects the active region K.The buried insulating layer 74 disposed on the buried word line 70configured to fill the trench 65 is disposed under the exposed portion.

Next, as shown in FIGS. 22A and 22B, sidewalls 88 may include a siliconnitride layer to cover inner walls of the capacitor contact openings 87.After forming the sidewalls 88, N-type impurity ion, such as phosphorusion, is introduced into the surface of the semiconductor substrate 50,thereby forming a high-concentration N-type impurity diffusion layer 90near the surface of the semiconductor substrate 50. The resultanthigh-concentration N-type impurity diffusion layer 90 functions as asource or drain region of a recess-type transistor according to the oneembodiment of the present invention.

Next, as shown in FIGS. 23A and 23B, a P-containing polysilicon layer isdeposited and then etched back to leave the polysilicon layer in a lowerportion of the capacitor contact opening 87, thereby forming a lowerconductive layer 91. Afterwards, a silicide layer 92 may include cobaltsilicide (CoSi) on the surface of the lower conductive layer 91. A metallayer 93, such as a tungsten layer, is deposited to fill the capacitorcontact opening 87. The resultant structure is planarized using a CMPprocess until the surface of the deposition layer 85 is exposed, so thatthe metal layer 93, such as the tungsten layer, can be remained onlywithin the capacitor contact opening 87. Thus, a capacitor contact plug95 with a triple layer structure may be formed.

Also, in the structure of the one embodiment of the present invention,as shown in FIGS. 23A and 23B, the capacitor contact plug 95 is formedover the high-concentration impurity diffusion layer 90 disposed betweenadjacent buried word lines 70 The bit line 81 is formed over thehigh-concentration impurity diffusion layer 77. Thus, the capacitorcontact plug 95 and the bit line 81 are finely disposed over the buriedword line 70 of the trench structure, thereby contributing tominiaturization.

Next, a tungsten nitride (WN) layer and a tungsten layer aresequentially deposited and patterned, thereby forming a capacitorcontact pad 96 shown in FIGS. 24A and 24B. The capacitor contact pad 96is connected to the capacitor contact plug 95.

Next, as shown in FIGS. 25A and 25B, after a stopper layer 97 mayinclude a silicon nitride layer to cover the capacitor contact pad 96, athird interlayer insulating layer 97 may include a silicon oxide layer.

Thereafter, as shown in FIGS. 26A and 26B, an opening 99, which is acontact hole, is formed through the third interlayer insulating layer 98and the stopper layer 97 to expose the top surface of the capacitorcontact pad 96. Afterwards, a lower electrode 100 of a capacitor mayinclude titanium nitride to cover an inner wall of the opening 99. Alower portion of the lower electrode 100 is connected to the capacitorcontact pad 96.

Next, as shown in FIGS. 27A and 27B, after a capacitor insulating layer101 is formed to cover the surface of the lower electrode 100, an upperelectrode 102 of the capacitor may include titanium nitride. Thus, acapacitor 103 may be formed. The capacitor insulating layer 101 mayinclude zirconium oxide (ZrO₂), aluminum oxide (Al₂O₃), hafnium oxide(HfO₂), or a stacked layer thereof.

Next, as shown in FIGS. 28A and 28B, after a fourth interlayerinsulating layer 105 may include a silicon oxide layer to cover thesurface of the upper electrode 102, an upper metal interconnection 106may include aluminum (Al) or copper (Cu). Afterwards, a surfaceprotection layer 107 is formed. As a result, as shown in FIGS. 28A and28B, a semiconductor memory device 110 having the same structure as thesemiconductor memory device 1, which is a DRAM, shown in FIGS. 1, 2A,and 2B is completed.

In addition, FIG. 29 shows a planar structure of a partialinterconnection structure of the semiconductor memory device 110obtained according to the above-described fabrication method.

The interconnection structure of FIG. 29 shows the insulating layer 82and the liner layer 83 disposed on both sides of the bit lines, whichare omitted from the interconnection structure of FIG. 1. FIG. 29clearly shows the capacitor contact plug forming region 17 definedbetween the bit lines 81 adjacent to each other in the Y direction

In view of the capacitor contact plug forming region shown in FIG. 29,it can be clearly understood that the capacitor contact opening 87described above with reference to FIGS. 22A and 22B is precisely formedby an SAC technique using the liner layer 83 as sidewalls. The capacitorcontact plug 95 is formed using the capacitor contact opening 87.

FIGS. 30A and 30B show an example of a structure of a semiconductormemory device including a saddle fin cell transistor instead of thesemiconductor memory device 1 including the recess channel celltransistor described above with reference to FIGS. 1, 2A, and 2B.

A semiconductor memory device 111 according to the one embodiment of thepresent invention is substantially the same as the semiconductor memorydevice 1 according to the previous embodiment except for the celltransistor.

FIG. 30A is a cross-sectional view corresponding to line A-A′ of thesemiconductor memory device 1 of FIG. 1, and FIG. 30B is across-sectional view corresponding to line B-B′ of the semiconductormemory device 1 of FIG. 1. The semiconductor memory device 111 accordingto the one embodiment of the present invention schematically includes acell transistor forming region 2A and a capacitor forming region 3 shownin sectional structures of FIGS. 30A and 30B.

In the semiconductor memory device of the one embodiment of the presentinvention, an electrode of a side contact portion 13 a, which contacts aside surface of the a high-concentration impurity diffusion layer 22, isformed in a buried line 13A to overlap element isolation trench 4. Thus,a convex portion 5A formed in the surface of a semiconductor substratelocated between the side contact portion of electrodes 13 a adjacent toeach other in a Y direction of FIG. 30A is used as a channel region,unlike in the cell transistor of the semiconductor memory device 1 ofthe previous embodiment.

FIGS. 31 and 32 are diagrams illustrating a process of fabricating asaddle fin cell transistor according to the one embodiment of thepresent invention.

Like the semiconductor memory device 1 according to the embodimentdescribed above, according to the method described with reference toFIGS. 3A through 7B, a method of fabricating the semiconductor memorydevice 111 according to the one embodiment of the present inventionincludes the following processes. A silicon nitride layer 62 for a maskand a carbon layer 63 which is an amorphous carbon layer aresequentially deposited on a semiconductor substrate 50 as shown in FIGS.7A and 7B. A pattern for forming gate-electrode trenches, which aretrenches, is formed as shown in FIGS. 7A and 7B. The semiconductorsubstrate 50 is dry etched as shown in FIGS. 31A and 31B, therebyforming trenches 115, which are gate-electrode trenches. As in theembodiment described above, the trenches 115 are formed in line-shapedpatterns extending in a predetermined direction, which is the Ydirection of FIG. 1. The predetermined direction intersects activeregions K.

In the embodiment described above, the silicon layer of thesemiconductor substrate is etched to a greater depth than the elementisolation trench as shown in FIGS. 8A and 8B. Conversely, in the oneembodiment of the present invention, the element isolation trench 53 isetched to a greater depth than the trench 115 of the semiconductorsubstrate 50, so that a convex portion 50A can be formed on thesemiconductor substrate 50 and used as a channel region of a celltransistor.

Afterwards, in the same manner as described in the embodiment withreference to FIGS. 9A and 9B, a gate insulating layer 67, a titaniumnitride layer 68, and a tungsten layer 69 may be formed and etched back.Hence, a buried word line 116 or a buried line 117 within the trench,which are the gate-electrode trench, is formed as shown in FIGS. 32A and32B. Thus, subsequent processes of the process shown in FIGS. 11A and11B are sequentially performed on the resultant structure of FIGS. 32Aand 32B like in the embodiment described above, thereby fabricating thesemiconductor memory device 111 having the sectional structure shown inFIGS. 30A and 30B.

In the semiconductor memory device 111 having the saddle fin celltransistor according to the one embodiment of the present invention, thechannel region is a portion of the convex unit 50A formed in the surfaceof the semiconductor substrate 50. Also, the channel region is widerthan in the semiconductor memory device 1 according to the embodimentdescribed above. Accordingly, the saddle fin cell transistor accordingto the one embodiment of the present invention may allow the flow of alarger current as compared with the recess-type transistor according tothe embodiment described above.

As used herein, the following directional terms “forward, rearward,above, downward, vertical, horizontal, below, and transverse” as well asany other similar directional terms refer to those directions of anapparatus equipped with the present invention. Accordingly, these terms,as utilized to describe the present invention should be interpretedrelative to an apparatus equipped with the present invention.

Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments.

The terms of degree such as “substantially,” “about,” and“approximately” as used herein mean a reasonable amount of deviation ofthe modified term such that the end result is not significantly changed.For example, these terms can be construed as including a deviation of atleast ±5 percents of the modified term if this deviation would notnegate the meaning of the word it modifies.

It is apparent that the present invention is not limited to the aboveembodiments, but may be modified and changed without departing from thescope and spirit of the invention.

What is claimed is:
 1. A semiconductor device comprising: asemiconductor substrate; an impurity region in the semiconductorsubstrate; and a conductive layer contacting a top surface of theimpurity region and at least a side surface of the impurity region.